Electric wave signaling system



I Dec. 27, 1927. 1,653,878

J. c. SCHELLENG ELECTRIC WAVE SIGNALING SYSTEM Filed Dec. 22. 1923 Patented Dec. 27, 1927.

UNITED STATES PATENT OFFICE.

JOHN G. SCHELLENG, or EAST oRANeE, NEW JERSEY, ASSIGNOR 'ro WESTERN ELEG- TRIO comrANY, INCORPORATED, OF NEW YORK, N. 2., A CORPORATION or NEW YORK.

ELECTRIC WAVE SIGNALING SYSTEM.

Application filed December 22, 1923. Serial No. es2,1s1.

This invention relates to electric wave signaling and more particularly to transmission and reception of signals by means of waves modulated in frequency.

It is well known that the energy of alternating currents may be utilized for the transmission of complex signals such as, for example, speech sounds. In general, systems designed to transmit signals by means of alternating currents have utilized energy of substantially constant frequency and modified this energy in accordance with signals by varying the amplitude thereof. The present invention employs a method of modulation whereby signal characteristics are imparted to alternating currents either by varying their amplitude or by varying their frequency.

More specifically, it is an object of this invention to variably impede the flow of alternating currents in accordance with signals to produce either amplitude or frequency variations of said currents.

Another object of the invention is to receive electric wave energy having either amplitude or frequency modulations and to obtain under control of said energ electric currents varying in amplitude in accordance with si nals.

Another 0 ject of the invention is to receive electric waves of a normal or carrier frequency modulated in accordance with signals, said modulation consisting of frequency variations, and to act on said waves in such manner that the value of the ratio of change of frequency to the normal frequency is increased or magnified.

A feature of this invention concerns a space discharge modulator arranged to produce electrical oscillations and having means for variably impeding said oscillations, said means comprising a space discharge device.

Another feature of the invention relates to a stifily resonant circuit for increasing the range of frequency variation obtainable by means of space discharge modulator.

A further feature of the invention comprises coupling means connected in the path of oscillatory currents produced by a vacuum tube generator which may be adjusted to match the impedance of the input circult of the generator. By thus adjusting the impedance of the input circuit and the coupling means either variations of frequency or variations of amplitude of the oscillatlons may be produced by variations of impedance in the input circuit. By proper ad ustment also the maximum range of frequency variation may be obtained.

A further feature of the invention consists of a receiving system for receiving frequency modulated waves in which means is provided for increasing or magnifying the value of the ratio of the range of frequency variation to the normal frequency.

Another feature of the invent-ion relates to a receiving system having a resonant circult adjuste to produce currents having amplitude variations corresponding to frequency variations of the received waves.

In one arrangement for carrying out this invention a vacuum tube oscillator is provided which is coupled to an antenna for the purpose of radiating energy. A vacuum tube modulator has its output circuit coupled to the input circuit of the oscillator by. means of an adjustable auto-transformer. A microphone transmitter is provided for varying the potentials impressed upon the grid of the vacuum tube modulator. Under the action of the signal current from the transmitter, the impedance of the output circuitof the modulator is varied and causes similar variations in the impedance of the path of the oscillatory currents in the generator. By adjustment of the auto-transformer these variations of impedance may be caused to produce either frequency variations or amplitude variations of the oscillatory currents. The energy transmitted from the antenna may be received by a sec- 0nd antenna coupled to a vacuum tube detector and also to a local source of oscillations arranged to produce an intermediate frequency in the detector which intermediate frequency is impressed upon a resonant circuit. This resonant circuit is so tuned that frequency variations of the impressed energy will produce amplitude variations in the currents established in the resonant circuit. These currents are impressed upon a second detector and cause the actuation of a receiver in its output circuit.

Embodiments of the invention are illustrated in the drawings as follows:

v (lonsequently,

Fig. 1, a transmitting system for producing either frequency or ampiltude modulations.

Fig. 2, a receiving system arranged to receive either frequency or amplitude modulated energy.

In the system of Fig. 1, a transmitter 10 in series with a battery 11 is connected to the terminals of primary 12 of transformer 13. The secondary 14 of this transformer is connected to the input circuit of a modulator 15 comprisin a vacuum tube 16 having a grid plate and lilament. A battery 18 is connected in the input circuit of tube 16 to supply a polarizing potential to the gr d of the tube. Resistance 19 is connected in shunt to the secondary winding 14 to supply a stabilizing impedance. The output circult of tube 16, which is connected between the late and filament contains an auto-transormer winding 20 in series with plate battery 21.

The oscillator 22 comprises a three-electrode vacuum tube 23 having input and output circuits and resonant circuits. Included in the input circuit connected t the grid and filament is a portion of the WlIlCllIlg of transformer 20. A grid leak resistance 24 and a blocking condenser 26 are also cluded in this input circuit. The output C11- cuit of oscillator 22 is connected across the plate and filament of tube 23 and comprises a battery 27 in series with a choke coil 28. A resonant circuit 29 comprising variable condensers 31 and 32 and inductance 33 is connected between the input and output circuits of tube 23. A condenser 34 is connected between the resonant circuit 29 and the plate supply circuit, including choke coil 28 and battery'27, to prevent the flow of direct current through the resonant circuit. The path from the resonant circuit 29 to the grid of tube 23 comprises a series tuned circuit consisting of a small-capacity variable condenser 35 in series with an inductance 36. The values of the capacity 35 and inductance 36 are made such that the reactance of this circuit varies rapidly with change of frequency. The resonant circuit 29 is coupled to an inductance coil 38 having one terminal connected to ground and the other to an antenna 39.

The term normal frequency is used to desi ate the frequency generated by the osci lator 22 when the variable elements of the system have been adjusted to the proper operating values and no sound waves are ing impressed upon transmitter 10.

When speech sounds are impressed upon the transmitter 10, variations are produced in the current flowing through the primary coil; correspondin variations of electromotive force are in need in the secondary 14. the potentials impressed upon the grid of tube 16 undergo similar variations whereby the impedance of the space path of this tube is caused to vary in a like manner. The auto-transformer 20, which has a portion of its winding common to the output circuit of tube 16 and the input circuit of tube 23, serves in a sense as an impedance matching device whereby the impedance connected to the input circuit of tube 23 may be adjusted so that the greatest range of frequency variation may be obtainable. The space path between the filament and plate of tube 16 provides a variable shunt to the primary of the transformer 20 and by the variations of impedance of the space path the impedance of the secondary circuit of this transformer is caused to vary.

The frequency of oscillations produced by generator 22 is controlled by the variations of the impedance of the oscillatory path when the value of the impedance of the autotransformer 20 has certain values. When the impedance of the auto-transformer 20 is adjusted to other values, variations of this impedance will produce amplitude changes in the oscillatory currents. Thus by setting the auto-transformer 20 at the proper normal value of impedance, either amplitude or fre quency modulation may be obtained.

The modulated oscillatory currents in the resonant circuit 29 induce corresponding currents in the antenna circuit by means of the coupling between coils 33 and 38.

Series resonant circuit 35-36 may be tuned approximately to the frequency of oscillations normally generated in the oscillator 22. The reactance of this circuit varies rapidly with frequency in such manner that the range of frequency variation is increased. In other words, when the impedance of transformer 20 tends to decrease the frequency, the reactance of series tuned circuit 3536 assumes a value which aids the action of the change of impedance in still further reducing the frequency. On the other hand, when the change of impedance of transformer 20 is such as to increase the frequency of oscillations, the reactance of the series tuned circuit tends to change in such manner as to aid the action of transformer 20 in still further increasing the frequency.

Referring to Fig. 2, an antenna 40 is connected to ground in series with an inductance coil 41. Coupled to the coil 41 is another coil 42 havingits terminals connected to a source of oscillations 43 arranged to produce a beat or intermediate frequency with the incoming waves. A detector 44 receives energy from the antenna 40 by the coupling between coil 41 and coil 45 which latter coil in conjunction with variable condenser 46 constitutes a resonant circuit.

The detector 44 comprises a vacuum tube 47, the grid and filament of which are connected to the resonant circuit 45-46. The

grid circuit of tube 47 includes a leak resistance 48 in shunt to a blocking condenser 49 whereby the proper biasin potential may be impressed upon the gri The output circuit of tube 47, which is connected between its filament and plate, is supplied with energy by a battery 51 in series with a choke coil 52. A resonant circuit 53 comprising an inductance coil 54 and a variable eondenser 55 is common to the output circuit of tube 47 and the input circuit of the tube 56 of a second detector 57.

The input circuit of the latter tube 1ncludes a grid leak resistance 58 and a blocking condenser 59 for impressing the blasing potential upon the grid of this tube. The output circuit of the tube 56 contains a receiver 60 in series with a battery 61.

Electric wave energy having amplitude or frequency modulations in accordance with signals may be received by antenna 40. The energy of this frequency is transmitted to the input of detector 44 by means of resonant circuit 45-46 which is tuned to the normal frequency of the received enfrequency represented by the difference or the sum of an intermediate frequency resulting from detection and the mean of the range of frequency variations. When this resonant circuit is so tuned, energy, having frequency variations, impressed thereon produces currents in the circuit which vary in amplitude in accordance with the variations of frequency of the impressed waves. Accordingly, variations in electromotive force corresponding to signal variations are impressed upon the grid of the second detector 57. Thus signal currents appear in the output circuit of this detector and actuate receiver 60.

Although this invention has been illustrated in connection with antennae, it is ap-' parent that it is equally adapted to signaling over wires. The embodiments disclosed are therefore not to be construed as limiting the scope of the invention which is defined only by the appended claims.

What is claimed is:

1. In an electric wave signaling system, means for transmitting energy having frequency modulations, means for receiving said energy and obtaining signals therefrom, said transmitting means comprising means for variably impeding the energy of oscillations comprising an auto-transformer connected to a vacuum tube modulator.

2. In an electric wave signaling system, transmitting means and receiving means, said transmitting means comprising a source of oscillations, a variable impedance for varying the frequency of said oscillations in accordance with signals, and means traversed .by said oscillations responsive to the frequency thereof for automatically extending the range of frequency variations.

3. In a system for transmitting and receiving frequency modulated electric wave energy, a modulator comprising a source of oscillations, means for varying the frequency of said oscillations in accordance with signals, a reactive path, and means for impressing said frequency varied oscillations upon said reactive path which independently extends the range of frequency variations produced by said frequency varying means.

4. A vacuum tube oscillator comprising an input circuit, an output circuit and a plurality of resonant circuits, means for causing variations in the frequency of the oscillations in accordance with signals, one of said resonant circuits comprisin an inductance and capacity in series, so ad usted that variations in the frequency of oscillations therein produce changes in the reactance thereof, which changes automatically magnify the frequency variations of said oscillations.

5. The method of signaling which oomprises producing oscillations of substantially constant amplitude, variably impeding said oscillations to vary the frequency thereof in accordance with signals and automatically impeding said oscillations in accordance with these frequency variations to extend the range of said variations, transmitting and receiving the energy of said oscillations and obtaining therefrom oscillations having amplitude variations corresponding to the frequency variations of the received energy.

6. In a radiant energy signaling system, an antenna, an oscillation generator coupled to said antenna, an auto-transformer traversed by oscillations from said generator, a signal controlled modulator arranged to vary the impedance of said transformer, and means for adjusting said impedance to values such that the variations of impedance produce either variations of frequency or variations of amplitude of said oscillations.

7. In a high frequency signaling system, a transmitting conductor, an oscillation generator coupled thereto, said generator having input and output circuits, a signal controlled modulator having an output circuit coupled to said input circuit, means for matching the impedance of said last named input and output circuits whereby the maximum range of variation of the frequency of oscillations generated may be obtained for a given impedance variation in said modulator.

8. A vacuum tube oscillator comprising an input circuit, an output circuit, said input circuit comprising means for varying the phase of the grid voltage which thereby varies the frequency of oscillations, said input circuit consisting of a series resonant circuit from the grid to a point of the output circuit and a portion of an auto-transformer between grid and filament, a space discharge modulator havin an anode circuit comprising a portion 0? said auto-transformer, a source of signals controlling the grid voltage of saidinodulator to thereby control the fre uency of oscillations generated by said osci later.

9. The method of wireless telephony in which, at a transmitting station, irequency fluctuations of a carrier wave are effected in JOHN C. SCHELLENG. 

